1. Field of the Invention
This invention relates to remocon (remote control) locator signal transmitting circuits, and more particularly to a remocon locator signal transmitting circuit provided in a television (TV) receiver, video cassette tape recorder (VCR) or the like, possessing, for example, a remocon locator function.
2. Description of the Prior Art
The remocon locator function means a function to issue a light or sound location notification signal from a remocon transmitter when it receives a radio wave (locator signal) transmitted by an apparatus main body thereby making clear a place where the remocon transmitter exists.
A conventional remocon locator signal transmitting circuit 1, as shown in FIG. 3, includes a transistor T1, having a base to which a locator code signal is applied from a control circuit (not shown). A control signal inverted by the transistor T1 is supplied to a base of a transistor T2 through a resistor R1, and also to an emitter of the transistor T2 through the resistors R1 and R2. The control signal is passed through the transistor T2 as a switch is supplied to a base of a transistor T3 through a resistor R3. When the control signal applied to the transistor T3 base is at a high level, a low level output is given to a printed circuit board (PCB) loop antenna 2. When the control signal to the transistor T3 base is at a low level, a high level output is supplied to the PCB loop antenna 2. An LC oscillation circuit is formed by the PCB loop antenna 2, a variable capacitor C1, and capacitors C2, C3 and C4 whereby a locator radio wave is transmitted from the PCB loop antenna 2. In this LC oscillation circuit the PCB loop antenna 2 acts as a reactance so that the frequency of the locator radio wave can be set at a predetermined frequency (390 MHz) by varying the capacitance of the variable capacitor C1. This predetermined frequency is assigned by the FCC (Federal Communications Commission), and a time period for which a radio wave is issued is specified within 4.9 seconds.
In this prior art, however, it has been necessary to adjust oscillation frequency on each assembly unit basis while taking into account circuit element characteristics. This is because a radio wave frequency has to be set by varying the capacitance of the variable capacitor C1. As a result, there have been problems in adjusting the oscillation frequency.
Furthermore, the capacitors C3 and C4 must be set in characteristic reverse to that of the transistor T2 in order to suppress temperature drift.
Moreover, it is necessary to use a glass epoxy PCB to stabilize the oscillation frequency at a predetermined frequency, resulting in higher costs.
Therefore, it is a primary object of the present invention to provide a remocon locator signal transmitting circuit which is inexpensive but stable in oscillation frequency.
A remocon locator signal transmitting circuit, according to the present invention, provided in an apparatus having a television tuner including a local oscillation circuit, comprises: a first input terminal for receiving an local oscillation signal with a predetermined frequency from the local oscillation circuit; a second input terminal for receiving a locator code signal; a modulating means for modulating the local oscillation signal by means of the code signal to output a locator signal; and a radio wave transmitting means for transmitting the locator signal as a radio wave.
Also, an electronic apparatus according to the present invention, comprises: a television tuner; a local oscillation means provided in the television tuner; a first input terminal for receiving a local oscillation signal from the local oscillating means; a second input terminal for receiving a locator code signal; a modulating means for modulating the local oscillation signal by means of the code signal to output a locator signal; and a radio wave transmitting means for transmitting the locator signal as a radio wave.
In the present invention, if a power for an electronic apparatus having the television tuner including the local oscillation means is turned on, the local oscillation signal is set in frequency at a predetermined frequency (390 MHz), for example, by a frequency setting means. Accordingly, an oscillation signal with the predetermined frequency is extracted at the local oscillation circuit onto the first input terminal. This oscillation signal is mixed (amplitude-modulated) with the locator code signal given onto the second terminal by the modulating means. This amplitude-modulation provides a locator signal by which a radio wave is transmitted from, for example, a PCB loop antenna to the remocon transmitter.
In the present invention, because a locator signal is created by utilizing a local oscillation signal obtained at the local oscillation circuit included in the television tuner, the component parts used is reduced in number and cost is low. Also, if the local oscillation circuit of the television tuner is configured for example by a PLL, frequency setting is easy and temperature drift is extremely low. Thus the frequency of the locator signal is stabilized.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.